Polymeric micelles are self-assembled amphiphilic block copolymers. These micelles have attracted attention as promising colloidal drug delivery systems (V. P. Torchilin J. Controlled. Release. 2001, 73, 137; C. Allen, D. et al., Colloids and Surfaces B: Biointerfaces 1999, 16, 3; and H. Otsuka, et al., Current Opinion in Colloid & Interface Science 2001, 6, 3). In these colloidal systems, the hydrophobic block typically forms the core, essentially a “microcontainer” for a lipophilic pharmaceutical (K. Kataoka, et al., Adv. Drug Delivery Rev. 2001, 47, 113). The hydrophilic part forms the outer shell, stabilizing the interface between the core and the external aqueous environment. Compared to traditional micellar systems, these polymeric surfactant-based drug carriers display apparent advantages such as lower critical micelle concentration (CMC), improved bioavailability, reduction of toxicity, enhanced permeability across the physiological barriers, and substantial changes in drug biodistribution.
Amphiphilic star-like macromolecules (ASMs) have also been studied for drug delivery applications. (See, e.g., U.S. patent application Ser. No. 09/298,729 filed Apr. 23, 1999; U.S. patent application Ser. No. 09/422,295, filed Oct. 21, 1999, and International Patent Application US00/10050 filed Apr. 18, 2000). The core-shell, amphiphilic structure of ASMs is covalently linked, which makes it thermodynamically stable compared to conventional micellar systems. Thus, ASM's offer numerous advantages over conventional micellar systems. Despite these advantages, the use of ASM's is somewhat limited due to the difficulty and cost associated with their preparation. Accordingly, there is a need for additional micellar systems and reverse micellar systems that possess some of the advantages associated with the thermodynamic stability of ASM's, but which are easier and less expensive to prepare.